1. Field of Invention
The present invention relates to a system for measuring concentricity and diameter of cable and wire. More particularly, the invention relates to a system and method for non-contact measurement of concentricity and diameter of cable and wire.
2. Related Art
During the manufacture of insulated cable and wire, it is desirable to insure that the conductor (e.g., wire) is well centered within the insulating material which covers the wire. To measure the concentricity, it is most convenient to locate and quantify the outer periphery of the insulating material and then measure the location of the conductor within.
For this discussion, the conductor is made of a conducting inner material. An outer jacket will include the insulating material. The combination of the two will be called the cable. The difference between the location of the center of the conductor and the center of the outer jacket is defined as the eccentricity.
It is advantageous to utilize non-contact measuring devices in measuring cable as it is formed because the insulating material is warm, soft and easily damaged when it comes out of an extruder. Optical or magnetic devices are typically used for this purpose. During the forming process, the cable is constantly moving longitudinally in the extrusion process. The cable also experiences lateral movement because of vibration in the taught wire. Historically, the practice is to measure the outer insulation diameter and conductor location at the same point along the axis of the cable to gain the best reading of eccentricity.
The current thought is to employ optical and magnetic measuring devices which reside in the same measuring plane, and orthogonal to the longitudinal axis of the cable. Currently, it is thought if the planes are in separate locations along the axis of the cable, it is difficult to distinguish between true eccentricity and angular misalignment of the cable. The measuring devices would measure at the same time, otherwise, the cable can move laterally in the time interval and spoil the measurement.
A previous device as seen in U.S. Pat. No. 5,528,141 to Kyriakis discloses an optical plane and magnetic measuring plane, and speaks of measuring at the same point on the wire, but not necessarily simultaneously in the same plane. Another device seen in U.S. Pat. No. 7,068,359 to Studer discloses two magnetic sensor coils placed on either side of an optical plane. The coils are connected together in such a way that they form a single magnetic measuring plane coinciding with the optical measuring plane and determine field intensity in front of and back of the optical measuring plane correlating the field intensities to determine an active inductive measuring plane which coincides with the optical measuring plane. The concept is to measure at a single time reference.
There remains a need to improve the art. The present invention improves the art by providing a novel system of placing the measuring devices in separate longitudinally spaced areas in order to provide a reliable measuring system and one in which permits increased space for maintenance, repair and cleaning of parts.